first: good job!

But today i found something, what i would like to use. Maybe it's already possible but i don't know how.
Example: I visit Facebook. I want to allow scripts from www.facebook.com, makes the use easier. But there are also many pages, which uses facebook-widgets. I don't want to allow facebook on these pages. So i want to allow facebook only if i'm visiting facebook.com, but it should be blocked on any other page. At the moment facebook is allowed on every page. How can I define such a rule? Another example is google. Google should be allowed only if there stands google.com in my addressbar.
Could you help me? Thanks a lot!